GAL question - allow users to e-mail only visable GAL users.

[brucealeg]

Hi,
We are deploying Zimbra for an internal only mail project. I'd like to lock down the system to where you can only mail those users visible in the GAL.

It's very easy to make only a few users visible, but if our users figure out the e-mail syntax (user@something.com) they can just manually type another users e-mail address in and bypass this effort.

Is there a good way in Zimbra to prevent this?